Mechanisms of immunity to rotavirus, the major cause of dehydrating diarrhea in children, have proven elusive. Despite the fact the live attenuated vaccines induce protection against severe disease, we still don't understand fully how immunity to rotavirus works, or even have rock-solid correlates of immunity from clinical trials. Animal models have suggested a variety of contributing mechanisms. Conceptually, understanding intestinal immunity to rotavirus is very important, because rotavirus represents a prototypical viral infection of humans that is limited to the intestine. If we can understand mucosal immune mechanisms to rotavirus, we will understand a lot more about immunity in the gut that is relevant to a plethora of pathogens. We hypothesize that a dominant mechanism of rotavirus inhibition by the human immune response is rotavirus specific virus protein 6 (VP6) specific antibodies of the IgA isotype. We propose that polymeric VP6-specific IgA antibodies bind to double layered particles inside infected intestinal cells and inhibit viral transcription. This mechanism has never really been tested in clinical trials as a correlate or mechanism, because VP6-specific antibodies will not neutralize virus in a conventional inhibitory assay, and only IgA antibodies could mediate the effect during transcytosis in polarized cells. We have isolated a large panel of hundreds of human VP6-specific human monoclonal antibodies, and shown that the immunodominant antibody response of humans specifies a set of antibodies that bind to double layered particles at the point of five-fold symmetry, inhibiting egress of viral transcripts from the transcriptionally active particle. The goal of this application is to show 1) that polymeric IgA forms of these antibodies inhibit rotavirus in a physiological manner during basolateral to apical transcytosis, 2) that the apical recycling endosome is a critical part of the transycytotic mechanism related to inhibition, and 3) that we can develop an artificial bispecific antibody scFv construct that can deliver antiviral antibodies to the cell via the IgA receptor (pIgR) as a means of developing biologic inhibitors for use against any intracellular intestinal pathogen. The work in this application will study the role of a particular type of antibodies in the gut (IgA antibodies) on immunity to rotavirus, the most common cause of severe diarrhea in children. The work seeks to show that these special antibodies bind to "inside" parts of the virus when the virus and antibodies meet inside of infected cells in the gut. If we show that this method of killing virus does inhibit rotavirus, we will understand how rotavirus antibodies and vaccines work and we can use this knowledge to create vaccines that work in a similar manner against other pathogens.